4气门汽油机缸内滚流运动的LDA实验研究

４气门汽油机是车用汽油机主要的发展方向，其缸内空气运动的主要形式划滚流，与传统２气门发动机缸内的涡流运动不同，本用ＬＤＡ在一台单缸４气门汽油机上测量了缸内滚流运动，并借助于多维数值模拟计算了滚流的形成和演变规律，研究了规律的湍流特征。研究指出，滚流形成于压缩过程初期，以后随活塞动得以维持和发展；它在压缩末期衰减，畸变和破碎，使燃烧室内湍流强度显增加。     

提高四气门汽油机缸内滚流强度的研究

在四气门汽油机中,运用滚流运动组织快速燃烧过程或混合气分层稀燃过程,都需要提高滚流强度。作者在一台单缸四气门汽油机上,通过 Ｌ Ｄ Ａ 测量,研究了滚流的形成过程,提出了提高滚流强度的机理,并对进气道结构、燃烧室内进气门出口侧壁屏蔽对滚流运动强度的影响进行了初步研究。研究结果表明,在滚流形成过程中,缸内首先出现双涡旋结构,以后演变成为单涡旋结构的滚流运动。增加流经排气门侧的进气气流或抑制直接沿进气门侧缸壁流入气缸的气流,都能提高滚流强度。     

4气门发动机单气门工作时罐内滚流运动的稳态测量研究

在稳流气道试验台上用叶片风速仪测量了4气门发动机单气门工作时缸内的滚流运动。确定了最大滚流矢量的位置;用热线风速仪研究了罐内滚流的形成过程,发现滚流轴线与水平面的夹角随气门升程的增大而增大。此时形成的“滚流”并非纯粹的滚流,而是斜轴涡流。     

2气门汽油机滚流进气系统的稳流实验研究

滚流（ｔｕｍｂｌｅ）本来是多气门发动机中应用的一种用于改善发动机性能的空气运动形式,其原因在由滚流生成的紊流具有尺度大,强度高的特点,可对汽油燃烧产生的有利影响,２气门汽油机一般不具备多气门发动机那样的进排气道侧布置的条件,这为滚流在２气门汽油机上的应用造成障碍。本文作者着眼有于目前国内的实际发动机生产水平,摸索了几种２气门汽油机中产生滚流的方案,通过稳流实验及性能实验证明２气门发动机中同样可以产     

四气门柴油机缸内流场LDA实验数据的分析研究

在一台经过改装的105单缸四气门柴油机上，由电机倒拖，使用激光多普勒测速仪（LDA）测量了缸内上部在进气和压缩过程的速度信号，分别使用小波分析法和集总平均法对进气和压缩过程中缸内的流场的平均速度和湍流强度进行了计算比较。小波分析结果中，对不同小波函数及小波分解层数分析结果进行了讨论。结果表明，在进气过程中，各尺度下的湍流强度值均较大，在压缩过程中，湍流强度值减小，使用集总平均法得到的湍流强度值大于小波分析法得到的结果。而且各不同尺度湍流强度变化曲线一致，说明各频段之间能量变化一致。     

四气门汽油机缸内滚流运动的LDA实验研究

为了研究丰田 8A汽油机缸内气流运动状况 ,将一台Cagiva3 5 0单缸四气门汽油机重新设计改造成为与之相近的且可以进行激光诊断测试的试验样机 ,选取二氧化钛为示踪粒子 ,采用激光多普勒测速法 (LDA)研究了该样机在进气和压缩冲程缸内流场的变化情况 .研究结果发现 ,滚流在进气过程中就开始形成 ,并在实验所能实测的曲轴转角范围内一直保持 ,接近上止点时旋涡虽严重畸变 ,但仍未破碎为小尺度的湍流 .     

内燃机气缸内稳态滚流运动沿气缸圆周分布特性研究

采用内置式滚流测量装置对CA1102发动机的四种气缸盖进行了滚流测量试验,主要测量不同气门升程敢缸内无因次滚流比沿气缸圆周的分布情况,同时采用Ricardo方法计算了进气终了滚流比沿气缸圆周的分布情况。结果表明：要在全升程范围内形成方向稳定的滚流运动,必须对进气流采取适当的导流措施;气缸内气体的滚流运动强度沿气缸圆周基本按余弦或正弦方式分布,并且,不同进气系统结构的气缸盖所产生的气缸内滚流运动矢量方向不同。     

可变气门正时对柴油机缸内流动和燃烧的模拟研究

运用多维燃烧模拟程序KIVA-3V对4102BZLQ柴油机进行了模拟,通过改变气门正时(负气门叠开角NVO)和气门升程,研究了三种情况下缸湍流强度、涡流比和滚流比这些气体流动参数的变化规律和对缸内压力、温度、温度分布等燃烧参数的变化规律。计算结果显示,随着负气门叠开角的增加,残余废气量增加,最高燃烧压力和温度都有减小趋势;进气冲程湍流强度、涡流比和滚流比都减小,而压缩冲程变化比较复杂,但是温度分布变得不均匀。     

进气道稳流试验装置内三维流动特性的数值模拟

使用FLUENT商业软件，采用RNG κ-ε湍流模型，对稳定流动实验条件下，不同进气道角度时切向进气道一气门一气缸内的流场，在两种气门升程下进行了三维数值模拟；分析了气道一气门一气缸内气体的稳态流动特性；总结了不同气道角度、不同气门升程时气道和缸内气体流动的变化规律。随着气门升程的增加，气道角度对缸内涡流的影响增大，并且涡流和滚流相互抑制。     

四气门汽油机进气道流动特性的稳流试验研究

通过自行研制的稳流气道试验台研究了一台单缸四气门汽油机进气道流动特性及其产生涡流和滚流的能力，分别试验了双气门全开、单气门开和单切向气道三种方案。研究结果发现，该汽油机缸内几乎不存在大尺度涡流，而只存在滚流，当关闭其中一个气门后，会得到较强的涡流，加导气片后，其涡流更强，但流通能力比双进气门全开差。对于滚流比，单进气门比双进气门略有提高，但差别不大。     

Imposing resolved turbulence in CFD simulations

In large‐eddy simulations, the inflow velocity field should contain resolved turbulence. This paper describes and analyzes two methods for imposing resolved turbulence in the interior of the domain in Computational Fluid Dynamics simulations. The intended application of the methods is to impose resolved turbulence immediately upstream of the region or structure of interest. Comparing to the alternative of imposing the turbulence at the inlet, there is a large potential to reduce the computational cost of the simulation by reducing the total number of cells. The reduction comes from a lower demand for mesh resolution in the upstream part of the domain. The first method uses a modification of the source terms in the discrete Navier‐Stokes equations. In the second method, an actuator is used to impose the turbulence. The methods are tested, and the most accurate is shown to be the approach of modifying the source terms. None of the two methods can impose synthetic turbulence with good results, but it is shown that by running the turbulence field through a short precursor simulation, very good results are obtained. Copyright © 2011 John Wiley & Sons, Ltd.     

基于小波分析的湍流参数提取方法

在定容燃烧弹内，利用孔板平动法生成湍流，用热线风速仪测量容弹内的速度，用小波分析技术将湍流分解为具有不同频带的组分，方便地获得了湍流强度、湍流尺度、湍流能谱等湍流特征参数。对具有不同频带的湍流积分时间尺度进行详细研究，结果表明，整个湍流的积分时间尺度代表所有湍流涡的平均寿命，与湍流频率和湍流能量分布有关。     

A method for the determination of turbulence intensity by means of a fast response pressure probe and its application in a LP turbine

This paper describes the measurements and the post-processing procedure adopted for the determination of the turbulence intensity in a low pressure turbine (LPT) by means of a single sensor fast response aerodynamic pressure probe. The rig was designed in cooperation with MTU Aero Engines and considerable efforts were put into the adjustment of all relevant model parameters. Blade count ratio, airfoil aspect ratio, reduced massflow, reduced speed, inlet turbulence intensity and Reynolds numbers were chosen to reproduce the full scale LP turbine. Measurements were performed adopting a phase-locked acquisition technique in order to provide the time resolved flow field downstream of the turbine rotor. The total pressure random fluctuations are obtained by selectively filtering, in the frequency domain, the deterministic unsteadiness due to the rotor blades and coherent structures. The turbulence intensity is derived from the inverse Fourier transform and the correlations between total pressure and velocity fluctuations. The determination of the turbulence intensity allows the discussion of the interaction processes between the stator and rotor for engine-representative operating conditions of the turbine.     

定容燃烧弹内湍流特性的研究

在对定容燃烧弹内的湍流进行循环分辨分析的基础上 ,计算了湍流的强度、自相关系数、标准一维能谱密度以及泰勒微观时间尺度。同时研究了传统集平均湍流研究方法和循环分辨分析法两者具有较大偏差的根源 ,从频率成分和尺度大小两方面刻画了湍流脉动与集平均脉动之间的区别和联系。通过比较不同“时窗”宽度和不同“相关窗”宽度条件下计算出的湍流能谱、自相关系数等湍流参数 ,找到了“时窗”和“相关窗”各自比较合适的折中值。     

The spectrum of wind speed fluctuations encountered by a rotating blade of a wind energy conversion system

A point on a rotating wind turbine blade encounters turbulence whose characteristics are quite different from turbulence measured by a stationary anemometer. This is true for vertical as well as horizontal axis wind turbines. The spectrum of the observed turbulence is distored in several subranges of frequency in characteristic ways. The midfrequency region is depleted and the removed energy is distributed into the high frequency end of the spectrum. The resulting two-peaked continuous spectrum also contains narrow-band spikes of turbulence energy centered on the frequency of rotor rotation and multiples of that frequency. The statistics of gusts are expected to be distorted also.The rotational sampling effect is quantified using measurements of wind velocity at circular arrays of anemometers and measurements by laser and hotwire anemometers traversing crosswind circular paths. A simple theoretical model of the spectrum of turbulence which is rotationally sampled is developed. The model, which assumes homogeneous, isotropic turbulence, reproduces the observed spectral features and provides an analytic verification and extension of scaling relations using turbine and atmospheric length and time scales. All known theoretical models of the spectrum of a rotationally sampled turbulence field are compared with the spectra which are derived from rotationally measured turbulence.Implications for turbine design, siting and control are drawn. A nondimensional parametric analysis of the rotational turbulence effect suggests criteria for selecting rotor height above ground and rotor rotation rate and provides guidelines for optimizing a design once the preliminary turbine configuration has been established.     

Synthetic atmospheric turbulence and wind shear in large eddy simulations of wind turbine wakes

A method of generating a synthetic ambient wind field in neutral atmosphere is described and verified for modelling the effect of wind shear and turbulence on a wind turbine wake using the flow solver EllipSys3D. The method uses distributed volume forces to represent turbulent fluctuations, superimposed on top of a mean deterministic shear layer consistent with that used in the IEC standard for wind turbine load calculations. First, the method is evaluated by running a series of large‐eddy simulations in an empty domain, where the imposed turbulence and wind shear is allowed to reach a fully developed stage in the domain. The performance of the method is verified by comparing the turbulence intensity and spectral distribution of the turbulent energy to the spectral distribution of turbulence generated by the IEC suggested Mann model. Second, the synthetic turbulence and wind shear is used as input for simulations with a wind turbine, represented by an actuator line model, to evaluate the development of turbulence in a wind turbine wake. The resulting turbulence intensity and spectral distribution, as well as the meandering of the wake, are compared to field data. Overall, the performance of the synthetic methods is found to be adequate to model atmospheric turbulence, and the wake flow results of the model are in good agreement with field data. An investigation is also carried out to estimate the wake transport velocity, used to model wake meandering in lower‐order models. The conclusion is that the appropriate transport velocity of the wake lies somewhere between the centre velocity of the wake deficit and the free stream velocity. Copyright © 2013 John Wiley & Sons, Ltd.     

Combined effect of grid turbulence and unsteady wake on convective heat transfer around a heated cylinder

Experiments are conducted to investigate the effects of free stream turbulence and unsteady wake on convective heat transfer of a heated cylinder. To serve as a heater, a stainless steel needs to be pasted on exterior surface of the bakelite test cylinder. In order to determine the heat transfer coefficient, 17 T-type thermocouples are placed in unequal distance around the circumference at the mid-span of the test cylinder. The range of Reynolds number is 30,000 to 120,000. The results and contributions of this study display that the higher wake passing frequency produces more frequent velocity fluctuations, more broad velocity profiles, and stronger degree of turbulence intensity which are caused by the upstream wake generator and turbulence grid to enhance the heat transfer.     

Near and far field flow disturbances induced by model hydrokinetic turbine: ADV and ADP comparison

Wake flows downstream of hydrokinetic turbines are characterized by hub and tip vortices, a velocity deficit and an increase in turbulence intensity. Velocity and turbulence recovery in the wakes of individual turbines constrains the density of turbines in an array and limits the amount of energy that can be produced by a turbine farm. However, few hydrokinetic turbine flow recovery studies have been conducted, especially on the far-field flow characteristics. Nor have studies evaluated the accuracy of acoustic Doppler profiler measurements in the wakes of turbines. The present study examines vertical profiles of mean velocity and turbulence, as well as longitudinal profiles of velocity deficit and turbulence levels measured at the symmetry plane of a model three-blade axial flow turbine in a large open channel flow. Mean velocity and turbulence statistics are measured using an acoustic Doppler velocimeter (ADV) and a pulse coherent acoustic Doppler profiler (ADP). ADV and corrected-ADP derived values of mean velocity, turbulence intensity and root-mean-square velocity constitute a well-documented data set that can be used to validate numerical models simulating the effects of hydrokinetic turbine arrays. We found that 80% of the flow recovery occurred about ten diameters downstream from the rotor plane, which suggests that practical values for longitudinal spacing of turbines should be between ten and fifteen diameters. Significant errors observed in mean velocity and turbulence statistics derived from ADP measurements in the near wake region raise concerns on the use of these instruments for such measurements in lab and field studies. Although the cause of some of the errors requires further investigation, we show that errors in turbulence intensity can be successfully corrected with supplemental ADV measurements.     

Visualization of a turbulent jet using wavelets

ho-cttonCoherent strUctUres are known to ealst and areresPOnsible for most of the momentUIn transfer inndulent jets. Many identification techniques, such asimage processing, sPeCtI'a analysis, spatial correlationfimctions, education schemes, PrOper OrthOgonaldecomposihon, stOChastic eshInation, pattem recoghhon,and wave1et tusform, are wen established to detennincoheret stI'Ucwts. Howevee the local scales with resPeCtto spacehme change continously for the turblence andthe coheren stheA…     

Systematic experiments on turbulent premixed Bunsen flames including turbulent flux measurements

The existence of good experimental data for turbulent premixed flames is of interest for the development and validation of numerical models. In this paper special focus is laid on the systematic variation of either the fuel-air ratio with fixed flow rate or varied flow and turbulence with fixed composition. In total, 15 different turbulent Bunsen flames are investigated. With the planar conditioned particle image velocimetry (CPIV) technique, simultaneous access is given to the flow, turbulence, and flame position data, using PIV for flow and turbulence and the density jump at the instantaneous flame front for reaction progress variable and density. This allows the fast determination of a large amount of statistical data such as Reynolds- and Favre-averaged mean reaction progress and velocities, which are needed for the density-weighted sets of equations used in the numerical codes. Additionally, conditioned and unconditioned mean velocities and velocity fluctuations can be determined and the turbulent flux terms of the reaction progress variable can be measured directly. Thus, a comprehensive data set is presented, which can be used for validation studies. The measured turbulent flux is compared with two models, the gradient diffusion assumption and a relation proposed by Veynante et al. that accounts for the competition between gas-dynamic expansion and turbulent mixing. While the former approach fails, the latter shows reasonable agreement for the radial flux and also accounts for the trend observed for the varied flow or flame conditions. The axial turbulent flux near the tip of the flame is not fully resolved.